The most common way to use Gaussian 16 for free is through your university or research institution. Many universities purchase campus-wide site licenses. Check with your department’s IT administrator or chemistry faculty to see if you can access Gaussian through: University laboratory computers.
If you are searching for a "free download" of Gaussian 16, it is important to understand the licensing structure immediately: It is not freeware, shareware, or open-source. gaussian 16 software download free